1. Field of the Invention
The present invention relates to a digital data delivery system. More particularly, this invention relates to a digital data delivery system that has a transmission facility for digitally transmitting at least one data piece including video signals or audio signals and a reception facility for receiving those signals.
2. Related Art
Presently, for example, an airplane for passenger transportation is equipped with an information system for providing passengers with various types of information for emergent use, entertainment use, etc. in its passenger room. According to one aspect, the information system is constituted as an information delivery system equipped with a transmission facility that stores information sources and appropriately delivers the information and a reception facility connected with the transmission facility via a wired and/or wireless transmission channel. The reception facility of the system has a reception facility body, an audio output device (e.g., headphone), and a video output device (e.g., liquid crystal display). The reception facility body is built into each seat and receives such as a video signal, an audio signal, a control signal, etc. and outputs the video signal and the audio signal to the video output device and the audio output device that are connected to the reception facility body. A passenger can enjoy the audio information and video information stored in the transmission facility or generated on the fly thereby with using the reception facility body built in the seat, the audio output device and the video output device.
In some cases, the video output device is provided on a rear face of a headrest of a seat. In this case, the video output device is adapted to output a video for a passenger who sits down behind the seat in which the connected reception facility body is built. Therefore, the reception facility body built in each seat outputs a sound to the audio output device for the passenger who sits down on the seat in which the reception facility body is built and outputs a video to the video output device for the passenger who sits down behind the seat which the reception facility body is built into.
JP-A-63-219289 discloses an information transmission device which can be applied to an information system used in the above-mentioned aspect. In the information transmission device according to JP-A-63-219289, a transmission facility multiplexes a plurality of analog video signals, analog audio signals, and analog control signals and transmits the multiplexed signals with one transmission channel. The transmitted signals are sent via a wireless transmission channel, which constitutes a part of the transmission channel, to the reception facility arranged in each seat. From the multiplexed signals, the reception facility selectively reproduces an audio for a passenger who sits down on the seat at which the reception facility is arranged and a video for a passenger who sits down on another seat behind the seat at which this reception facility is arranged.
In another conventional information supplying facility, there is provided an aspect in which a transmission facility and a reception facility are connected with each other with a digital wired transmission channel. In this aspect, information is digitally compressed and encoded by the transmission facility and multiplexed with a plurality of programs and services and then delivered as digital data through the wired transmission channel.
Information of the digitally compressed/encoded and multiplexed programs or services is selectively decoded by the reception facility built in each seat. In a case where the video output device is equipped on the rear face of each seat as in the case of an aspect described in JP-A-63-219289, the reception facility decodes data of a program or a service for a passenger seated behind the seat. Then, the reception facility outputs a video signal of the decoded program or service to the video output device connected to the reception facility. On the other hand, the audio signal of the program or service decoded by the reception facility is delivered again through the wired transmission channel, so that this decoded audio signal is received by another reception facility build in a seat behind that seat and output by the another reception facility to the audio output device connected thereto. That is, in the present example, each reception facility built in the seat decodes a set of video and audio data contained in a program or a service for the passenger seated on a seat behind the seat. Therefore, the audio data is decoded and then returned to the wired transmission channel, and the decoded audio data is transmitted to another reception facility arranged at a seat right behind, and output to the audio output device connected to the reception facility. A body that decodes data and a body that reproduces and outputs the same are thus made different from each other in order to keep synchronization between the decoded audio and the corresponding decoded video by relegating the decoding of the compressed and encoded audio and video data to one instrument of the reception facility.
In the aspect described above, a decoded audio signal is transmitted via a transmission channel. Therefore, in this aspect, a transmission channel employed (e.g., Ethernet connected with cables) may be obliged to transmit relatively large amount of information.
However, as a matter of course, equipping with wired transmission channels throughout the airplane's passenger room results in an increase in weight of the airplane. In addition, when changing a layout of the seats in the passenger room, the wired transmission channels are needed to be disconnected once near the seats, so that it is necessary to schedule much time for the change of the layout in an operational plan of the airplane. This results in a decrease in efficiency of the operation of the airplane. For this reason, it is greatly desired to provide a wireless transmission channel between a transmission facility and a reception facility arranged in each seat by using presently available digital broadcasting and communicating technologies.
However, a wireless transmission channel is not better than a wired one in view of its transmission capacity. Therefore, as a technological methodology, it is not desirable that a signal once decoded by one reception facility is transmitted again through the transmission channel so as to be received and reproduced by another reception facility, as in the case of the conventional art.
In order to avoid such problem, one technological methodology is naturally brought to our mind that decodes a compressed and encoded video signal of a program or service using a reception facility built in one seat and reproduces the same for a passenger sitting on a seat behind the seat and simultaneously, decodes and reproduces a compressed and encoded audio signal of the same program or service using another reception facility built in the back seat. However, in this case, reception facilities respectively receive compressed and encoded video and audio signals, and mutually independently, decode and reproduce the received signals, resulting in a concern for an asynchronous reproduction of the video signal and the audio signal.